Determining Elastic Constants and Indirect Tensile Strength from a Single-Orientation Core of Transversely Isotropic Rock by the Uniaxial Compression and Brazilian Tests

Abstract

ABSTRACT: A practical method determining five elastic constants of a transversely isotropic rock is proposed by the uniaxial compressive strength test and the Brazilian test using specimens from a single-orientation core. The indirect tensile strength of the Brazilian test can be obtained through this suggested method. The simple iterative procedure based on the least square method was suggested. While suggested method works best for inclined cores in determining five independent elastic constants, horizontally or vertically layered cores require the empirical relation to determine the second shear modulus. Validation against Asan gneiss shows that the proposed method determines five elastic constants with acceptable variation in comparison with those determined by the conventional method using multiple cores. The indirect tensile strength of the Brazilian test can be evaluated with the determined elastic constants as inputs, but it can differ depending on the method determining elastic constants. According to the observed variations in the experiment results, the better understanding of the mechanism of the Brazilian test and the further experimental validation are recommended. 1. INTRODUCTION Rock deformation and failure are often dependent on loading direction; as such, considering the mechanical anisotropy of rock is important in various civil, mining, and petroleum engineering applications. The anisotropic elastic constants have to be considered for in-situ stress measurement by the overcoring method (Van Heerden, 1983), design of underground structure (Sanio, 1985), and numerical modeling of hydraulic fracturing (Kahn et al., 2012). The tensile strength needs to be carefully determined for the stability analysis for mine roof (Nova and Zaninetti, 1990) and the design of drilling or rock excavation (Yarali and Kahraman, 2011); therefore, accurate determination of tensile strength is important. The transversely isotropic (TI) model has been commonly used to characterize anisotropic rock owing to its applicability and simplicity (Amadei, 1996; Exadaktylos, 2001).